The present invention relates to an image forming apparatus, such as a laser printer, and a scanner apparatus incorporated in the image forming apparatus.
An electrophotographic type laser printer incorporates a scanner unit for forming an electrostatic latent image on a photoconductor.
The scanner unit comprises a light beam emitting unit composed of a semiconductor laser, for example, and a polygon mirror for deflecting and scanning a light beam from the light beam emitting unit. The light beam emitted from the light beam emitting unit is deflected by the polygon mirror and scans a uniformly charged photoconductor at high speed to expose the photoconductor to light. Consequently, charges in the exposed portion of the photoconductor are removed, and an electrostatic latent image is formed on the photoconductor by a skewed distribution of charges.
Moreover, in such scanner unit, a cylindrical lens for focusing the light beam from the light beam emitting unit by converging it on one point on the deflecting plane of the polygon mirror is disposed between the light beam emitting unit and the polygon mirror. The cylindrical lens is formed in the shape of a substantially semi-cylindrical shape so that one surface in the light beam passing direction is made a convex surface, the other surface is made a flat surface, and the thickness between the surface top part of the one surface in the shape of a convex surface and the other surface becomes largest (see, for example, Japanese Examined Patent Application Laid-Open No. 5-47084 (1993)).